Filter skimming apparatus

ABSTRACT

Filter skimming apparatus comprising an elongated concave plunger arm adapted for telescopic insertion in a test tube. The plunger arm has an inverted cup-shaped piston head at the lower end for holding a filter element and having a rim for slidable sealing engagement of the inner walls of the test tube.

United States Patent Connelly et a1.

FILTER SKIMMING APPARATUS Inventors: John J. Connelly, San JuanCapistrano; Alan A. Di Stefano, Rialto, both of Calif.

Baxter Laboratories, Inc., Morton Grover, 111.

Filed: Apr. 5, 1973 Appl. No.: 348,372

Assignee:

U.S. Cl 210/359, 23/259,210/D1G. 23 Int. Cl 301d 33/00 Field of Search23/259; 210/359, D16. 23;

References Cited UNITED STATES PATENTS 12/1969 Farr 210/359 2/1970 Mass210/1316. 23

I Mar. 25, 1975 3,512,940 5/1970 Shapiro 23/259 3,586,064 6/1971 Brown23/259 X 3,661,265 5/1972 Greenspan 210/359 3,693,804 9/1972 Grover210/359 3,802,843 4/1974 Kim 23/259 Primary ExaminerMorris O. WolkAssistant ExaminerSidney Marantz Attorney, Agent, or FirmScott J. Meyer;Louis Altman [57] ABSTRACT Filter skimming apparatus comprising anelongated concave plunger arm adapted for telescopic insertion in a testtube. The plunger arm has an inverted cupshaped piston head at the lowerend for holding a filter element and having a rim for slidable sealingengagement of the inner walls of the test tube.

2 Claims, 13 Drawing Figures PZJENTED 3,873 ,449

sum 2 o 3 FILTER SKIMMING APPARATUS This invention relates to animproved filter skimming method and apparatus and, more particularly, toa method and apparatus for the separation of blood serum or plasma fromsuspended cells and other particulate matter.

The separation of serum or plasma from centrifuged, clotted or wholeblood specimens is a common clinical procedure. Various filter skimmingdevices have been adapted for such use. These devices are conventionallyprovided in the form of two telescoping tubes in which the outer tube isan initial blood collection test tube and the inner tube is a plungertube which serves as a pressure or vacuum filter and collects thesupernatant liquid as the plunger tube is depressed into the outer testtube. The plunger tube is provided with a filter at the bottom toocclude cells from the supernatant liquid during the skimming of thesupernatant blood serum or plasma from the suspended cells.

Illustrative of the foregoing filter skimming devices are those such asdescribed in US. Pat. Nos. 3,355,098; 3,481,471; 3,512,940; 3,661,265;and 3,693,804.

It is an object of the present invention to provide an improved filterskimming method and apparatus.

It is another object of this invention to provide a novel filterskimming method and apparatus for improved separation of blood serum orplasma from suspended cells and other particulate matter.

It is still another object of this invention to provide a convenientlyaccessible test tube size filter skimming apparatus comprising a thumboperable filter skimming plunger which is adapted to be telescopicallyinserted in a blood collection test tube whereby the resultingsupernatant liquid can be readily decanted after filtering.

These and other objects will be apparent to the person skilled in theart after reading the specification and claims hereof.

Briefly stated, the filter skimming apparatus of this inventioncomprises an elongated concave plunger arm adapted to be telescopicallyinserted in a test tube, an inverted cup-shaped piston head at the lowerend having a small bore opening at the top for allowing passage ofsupernatant liquid and a peripheral rim at the bottom for slidablesealing engagement of the inner walls of a test tube, and a lower cuphaving a small bore probe at the bottom for allowing entrance of fluidspecimen and an upper open cavity for retaining a filter element, theouter walls of said cup adapted for engagement of the inner walls ofsaid cup-shaped piston head.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter regarded as forming thepresent invention, it is believed that the invention will be betterunderstood from the following exemplary description taken in connectionwith the accompanying drawings in which:

FIG. 1 is an exploded view showing the elements of the filter skimmingdevice of the invention.

FIG. 2 is a perspective view showing the filter skimming device inoperation.

FIG. 3 is an end view of the plunger of the filter skimming deviceshowing the concave arm section, the peripheral rim and the small boreopening at the top of the piston head.

FIG. 4 is a side elevational view of the plunger in cross-section takenalong the line 44 of FIG. 3 showing the elongated, concave arm and thelower cupshaped piston head.

FIG. Sis an end view of the cap of the filter skimming device showingthe offset small bore probe.

FIG. 6 is a side cross-sectional view of the filter cup taken along theline 66 of FIG. 5 showing the small bore probe at the bottom and theupper open cavity.

FIG. 7 is a side view of a filter element for placement in the filtercup of FIG. 6.

FIG. 8 is a top view of the filter element of FIG. 7.

FIG. 9 is an end view ofa plunger in another embodiment of theinvention.

FIG. 10 is a side elevational view of the plunger in cross-section takenalong the line l010 of FIG. 9.

FIG. 11 is a side elevational view of a plunger in still anotherembodiment of the invention.

FIG. 12 is a front elevational view of the plunger of FIG. 11.

FIG. 13 is an enlarged fragmentary side crosssectional view of theplunger of FIG. 11 showing the piston head assembly with the filter cupand filter element.

Referring now to the drawings and particularly to FIG. 1, the filterskimming apparatus comprises plunger 10, a filter cup 20, and a filterelement 26. Plunger 10 has a relatively thin, for example l2 mm. thick,elongated arm 11 with side edges 12, an inverted cupshaped piston head13 at the lower end having a cavity 14, a top 15, and a lower peripheralrim 18 which is adapted for slidable sealing engagement of the innerwalls of test tube 29. Piston head 13 has a small bore opening 17preferably extending throughout a relatively short, upwardly disposedtubelike extension 16 and centered at the top 15 of piston head 13.

Filter cup 20 has a cavity 21, a bottom 22 and a probe 23 having a smallbore opening 24 and extending downwardly and preferably offset from thecenter of the bottom. Probe 23 preferably has a beveled edge such as ata 45 angle at opening 24. The outer diameter of filter cup 20 is suchthat the cup will fit tightly in piston head 13.

Filter element 26 has a top surface 27, a bottom surface 28 and issuitably proportioned for placement in the cavity 21 of filter cup 20,which in turn is adapted for insertion in'the cavity 14 of piston head13. The diameter of filter element 26 is such that the filter will fittightly in filter cup 20.

FIGS. 3 and 4 show the plunger 10 in greater detail. The elongated arm11 preferably gradually tapers in width as it extends from the pistonend to the distal end. Greater width is preferred at the piston end dueto stresses in operation of the plunger. Arm 11 is generally concave onits inner side to allow convenient thumb and finger gripping and canalso have a spoon shaped handle configuration.

The piston head 13 has a small bore opening 17 to allow upward passageof supernatant fluid. The bore preferably is about 0.03 to about 0.05and most preferably about 0.04 inch in diameter. Piston head 13preferably has a relatively short tubelike extension 16 to allow asteady upward flow rather than squirting of supernatant fluid throughopening 17. Thus, in an exemplary plunger arm having an overall lengthof about 4 inches, the extension I6 can be from about one-half to aboutone inch and preferably about three-fourth of an inch in height. Theopening 17 is centered in the top I5 of piston head 13 to allow an evenflow of supernatant fluid from cavity 14.

FIGS. 5 and 6 show the filter cup in greater detail.

The probe 23 has a small-bore opening 24 generally of about the samediameter as opening 17. Probe 23 is of a length suitable for extendingdownwardly through the surface of the fluid specimen in test tube 29. Asmall fraction of an inch such as about one-eighth to aboutthree-eighths and preferably about one-fourth inch one-eighth is asufficient length for convenient operation of the plunger. Probe 23preferably has a beveled edge which can be at about a 45 angle foroptimum cutting into the depth of the supernatant fluid. Probe 23 alsopreferably is positioned offset from the center of bottom 22 of cup 20and is thereby adapted to reach into an extensive portion of the fluidspecimen as the plunger 10 is gradually twisted in test tube 29.

Filter cup preferably has an annular projection which forms a ridge onthe inner bottom of the cup. Filter element 26 preferably isproportioned to seat on projection 25 and has a thickness substantiallyequivalent to that portion of the height of cup 20 above said projection25. Piston head 13 similarly preferably has an annular projection 19which forms a ridge on the inner top of the piston head with a diametersubstantially the same as the diameter of filter cup 20. Projection 19thereby restrains filter cup 20 from seating flush against the inner topof piston head 13. Thus, neither cavity 21 nor cavity 14 is completelyfilled with the filter element 26 and a pair of small, residual cavitiesare formed below the bottom surface 27 and above the top surface 28 offilter element 26. The lower said residual cavity allows the intake offluid specimen through probe 23 to be evenly dispersed over entirebottom surface of filter element 26 and the upper said residual cavityallows for uniform dispersion of the fluid specimen through the filterelement 26 and similar uniform collection of the filtered supernatantfluid at the top prior to its exit through opening 17.

FIGS. 7 and 8 show the filter element 26 prior to assembly in filter cup20. The filter element 26 is gener' ally cylindrical and can befabricated of various suitable filter materials such as glass-wool,asbestos, or synthetic plastic fibers, for example, compactedpolypropylene or other such polyolefin fibers; porous ceramic or othersuch inert inorganic filtering materials, for example, sintered glassand diatomaceous silica; porous plastic substances such as polyurethaneelastomeric foam and porous polyethylene. The pore size of the filterelement preferably is such as will effectively filter all fibrin strandsfrom a blood sample.

FIGS. 9 and 10 show another embodiment of the plunger. In thisembodiment, the small bore opening 37 is positioned offset from thecenter of the top 35 of piston head 33 and a relatively short tubelikeextension 36 traverses the lower end of elongated arm 31 intermediateside edges 32. The supernatant fluid which collects in the top part ofcavity 34 will thus flow through opening 37 and thence down the innerside of elongated arm 31. In this embodiment, arm 31 will have a greaterthickness at the piston end to allow space for tube 36 within theconfines of the arm. Tube 36 will have about the same height as tube 16in the embodiment of FIGS. 3 and 4. Rim 38 and projection 39 correspond,respectively, to rim 18 and projection 19 in the embodiment of FIG. 4.

FIGS. 11, 12 and 13 show still another embodiment of the plunger. Inthis embodiment, short tubelike extension 46 is positioned on the innerconcave side of plunger arm 41 intermediate both side edges 42. Pistonhead 43 has a lower peripheral rim 48 and a partial peripheral upper rim49 opposite the concave portion of arm 41, both of which rims makeslidable sealing engagement of the inner walls of a test tube.

FIG. 13 shows the piston head assembly in which filter element 53 ispositioned in the cavity of filter cup 51, which in turn is positionedin cavity 44 of piston head 43. Annular projection 50 on piston head 43restrains filter cup 51 whereby cavity 55 is formed between the top 45of piston head 43 and the top of filter element 53; annular projection52 on filter cup 51 similarly restrains filter element 53 whereby cavity54 is formed below filter element 53.

In the embodiment shown in FIG. 13, arm 41 has a small transverseopening 47 at the top of tubelike extension 46 whereby fluid can beejected on either or both sides of arm 41. In probe 56, the angle of thebeveled edge at opening 57 faces the opposite direction from that shownin the embodiment of FIG. 6. In assembly, probe 56 is in substantialvertical alignment with tubelike extension 46. To facilitate thisalignment in operation, the outer wall of filter cup 51 and the innerwall of piston head 43 can be provided with a vertically disposed keywayand a mating rib on either wall.

In still another embodiment of the present invention, the rim 18 forslidable sealing engagement of the inner walls of test tube 29 can beprovided on the periphery of bottom 22 of filter cup 20 instead ofpiston head 13.

Tubes 16, 36 and 46 preferably are of a clear material such as atransparent plastic so that the operator can determine whether any cellsare being collected in the filtered supernatant liquid. The entireplunger 10 can be conveniently fabricated of polyolefin plastic, forexample, polyethylene and polypropylene and other such plasticmaterials.

In the operation of the apparatus and in practicing the method of theinvention, as can best be seen from FIG. 2, the operator will grasp thedistal end of plunger 10 with the thumb positioned in the concave sideof elongated arm 11 and slowly depress the plunger into test tube 27until probe 23 reaches through the top surface of the fluid specimen.Due to the slidable sealing engagement of rim 18 with the inner walls ofthe test tube, pressure will be created which forces the serum or plasma61 into piston head 13 which contains the filter element. The filteredsupernatant liquid will then be forced through opening 17 and collect inthe top of test tube 27 above the rim 18. Plunger 10 can be depressed inthe fluid specimen to the extent desired and generally so that probe 23continuously extends into the supernatant fluid as the fluid is beingforced through the filter and until it finally reaches the surface ofthe red cells 60 packed at the bottom of the test tube. Rotation ofplunger 10 having an offset probe 23 will ensure collecting supernatantliquid trapped in any fibrin strands. After the entire portion of thesupernatant liquid has passed through the filter element and into theupper part of test tube 27, the filtered supernatant liquid can bereadily collected by decantation into another test tube or similar suchstorage container or it can be aspirated such as with a pipette.

The present invention has several unique advantages over filter skimmingdevices of the prior art. In the present device the filtered sample canbe retained within the walls of the same test tube in which it wascontained prior to filtering whereas in prior devices a separatetelescoping inner collection tube is generally required.

The lower probe on the filter cup in the present device, in addition toits function of reaching into the fluid specimen, is adapted to serve asa vent which is in alignment with the upper tubelike extension on theplunger arm to allow entrance of air below the piston head so that theplunger arm can be more readily withdrawn from the test tube than thetelescoping inner collection tubes of prior devices.

Not only is the present device suitable for manual use but also it iswell adapted for semi-automatic use such as on the sample turntables ofautomated analytical instruments, for example, the Technicon AUTOANA-LYZER. In such use, the sample on the turntable can be directlyaspirated out of the Vacutainer or sample tube by the sampler probe.This can be done without removal of the plunger arm.

In the preferred embodiment of FIGS. 11, 12 and 13, the presentinvention has a unique plunger pull-out feature. By tilting the entiresample test tube, the plunger arm with the transverse opening 47 can bewithdrawn in such a mananer that the supernatant filtered fluid iseasily and entirely retained above the lower unfiltered material. Inprior devices there generally is a continuum of fluid and withdrawal ofthe inner telescoping collection tube tends to cause back filtration.

In order to facilitate prevention of contamination of the filtered serumsample, the plunger arm (e.g., arm 11) can be provided with a lowercylindrical portion having a diameter about the same as that of thepiston head (e.g., piston head 13) anda height greater than that of thetubelike extension.(e.g., extension 16).

While particular embodiments of the invention have been illustrated anddescribed herein, it will be obvious to those having skill in the artthat various changes and modifications can be made without departingfrom the spirit and scope of the invention, and it is intended to coverin the appended claims all such changes and modifications.

What is claimed is:

1. Filter skimming apparatus comprising a plunger having an elongatedarm, an inverted cup-shaped piston head, a filter cup disposed in saidpiston and containing a filter element, said piston head having anannular projection on its inner top and said filter cup having anannular projection on its inner bottom whereby a cavity is formed abovesaid filter element and a second cavity is formed below said filterelement, said piston head having an upwardly disposed, small boretubelike extension and said filter cup having a downwardly extending,small bore probe offset from the center of the bottom of said filtercup, said plunger having a peripheral rim at the piston zone adapted forslidable sealing engagement of the inner walls of a test tube.

2. The filter skimming device of claim 1 in which the tubelike extensionis offset from the center of the top of said piston head toward theinner side of said elongated arm, the elongated arm is concave on itsinner side and contains a small transverse opening at the top of saidtubelike extension, and said peripheral rim is positioned on the lowerextremity of said piston head. l= =l

1. Filter skimming apparatus comprising a plunger having an elongatedarm, an inverted cup-shaped piston head, a filter cup disposed in saidpiston and containing a filter element, said piston head having anannular projection on its inner top and said filter cup having anannular projection on its inner bottom whereby a cavity is formed abovesaid filter element and a second cavity is formed below said filterelement, said piston head having an upwardly disposed, small boretubelike extension and said filter cup having a downwardly extending,small bore probe offset from the center of the bottom of said filtercup, said plunger having a peripheral rim at the piston zone adapted forslidable sealing engagement of the inner walls of a test tube.
 2. Thefilter skimming device of claim 1 in which the tubelike extension isoffset from the center of the top of said piston head toward the innerside of said elongated arm, the elongated arm is concave on its innerside and contains a small transverse opening at the top of said tubelikeextension, and said peripheral rim is positioned on the lower extremityof said piston head.